Y.H. Lee, Samsung's executive vice president of the mobile business, tells CNET that it's because it's less expensive and easier to do plastic than other materials.

"When Samsung looks at what materials to use, it isn't just taking into consideration the aesthetic quality of the device, Lee said," according to CNET. "The company also assesses how quickly and efficiently it can manufacture the product, knowing that it will have to ship a high volume."

This is sort of a duh, but in a weird way it's refreshing Samsung is just being honest about it.

It also uses plastic to make the backs of the phone removable, which it says is a big feature users like.